Method for producing an adsorption agent for treating compressed gas and an adsorption device provided with such an adsorption agent

ABSTRACT

A method for manufacturing an adsorption agent for treating compressed gas, which includes the steps of providing a monolithic supporting structure; producing a coating suspension that includes an adsorbent; applying the coating suspension on the supporting structure to form a coating; applying a thermal treatment to the coated supporting structure in order to sinter the coating.

The present invention relates to a method for manufacturing anadsorption agent for treating compressed gas, more specifically anadsorption agent that can be used for drying compressed gas, for examplecompressed air.

Adsorption devices are already known in the form of drying devices forcompressed gas, whereby these drying devices comprise a vessel in whicha drying agent, or desiccant, is placed. The vessel concerned isprovided with an inlet for supplying a compressed gas to be dried, andan outlet for removing dried gas.

The drying agent concerned is generally realised in the form of aregeneratable drying agent, or in other words a drying agent that can beregenerated after reaching a certain degree of saturation. It is indeedthe case that as the drying agent extracts moisture from the gas to bedried, this drying agent will become increasingly saturated withadsorbed moisture. Hence, it is usual, after using the drying agent fora certain time to dry compressed gas, to regenerate this drying agent,for example by exposing it to a regeneration gas flow that extracts themoisture from the drying agent. Such a regeneration gas flow can consistof a fraction of the dried gas and/or hot gas for example whose relativehumidity is sufficiently low to be able to realise the regeneration ofthe drying agent.

In some embodiments of drying devices for compressed gas, use is made oftwo or more vessels of drying agent. With two vessels this principle ofdrying device is also referred to as a twin tower dryer. In such a typeof drying device a compressed gas, for example originating from acompressor, can be passed through the first of the aforementionedvessels for example, where it will be dried by the drying agent in thevessel concerned, after having passed through an after cooler and acondensate separator (which may or may not form part of the after coolerconcerned). This vessel consequently acts as a drying vessel.

At the same time, a regeneration gas flow can be guided through a secondaforementioned vessel in order to regenerate the drying agent in thatsecond vessel by extracting the moisture from this drying agent. Thiscan be done by making use of a gas that has already been dried, forexample, that is tapped off downstream from the drying vessel forexample and/or by supplying a gas flow that has been heated, for exampleby recovering the heat generated in the compressor during thecompression. In this last case it is called a “heat of compression” orHOC dryer.

When the drying agent in the drying vessel has reached a certain degreeof saturation, the gas flows through the first and the second vessel canbe changed over, such that the drying agent in the first vessel will nowbe regenerated by a regeneration gas flow while the second vessel willtake on the role of drying vessel. In this way the two or more vesselswill alternately operate as a drying pressure vessel and a regeneratingpressure vessel, such that continuity in the drying process can berealised. Examples of such drying devices with a number of vessels aredescribed for example in US 2003/023.941, U.S. Pat. No. 4,783,432, U.S.Pat. No. 6,375,722, EP 1.776.171 and WO 2006/050.582.

The drying agent that is used in such drying devices with a number ofvessels often consists of grains of silica gel, activated alumina or amolecular sieve material, or a combination thereof. As is knownactivated alumina is produced by thermal dehydration or activation ofaluminium hydroxide Al(OH)₃, while molecular sieves consist of syntheticzeolites (crystalline aluminosilicates).

A limitation of such a type of drying device that comprises a dryingagent in a granular form, consists of the gas speeds through the vesselshaving to be limited in order to counteract grains moving against oneanother or even fluidisation. Indeed, due to the grains being set inmotion friction will occur between them, which in turn leads to dustformation and a reduced drying capacity. Other causes of such dustformation are for example pressure variations and/or thermal shocks.Moreover, the pressure drop across a twin tower dryer is relatively highand the desiccant grains have a rather high thermal mass.

Alternative drying devices are known for compressed gas, whereby thedrying agent is placed in a rotating drum, while a drying zone andregeneration zone extend in the vessel. During the operation of such adrying device, the drying drum will be made to rotate by drive meansprovided to this end, such that the drying agent in this drying drumwill alternately be taken through the drying zone and the regenerationzone. The compressed gas to be dried will be guided through the dryingzone, while the regeneration gas flow is guided through the regenerationzone, in order to realise simultaneous drying of compressed gas in thedrying zone and regeneration of the drying agent in the regenerationzone.

Examples of such drying devices that are provided with a rotating dryingdrum are described for example in WO 00/033.943, WO 00/074.819, WO01/078.872, WO 01/087.463, WO 02/038.251, WO 2007/079533, WO2005/070.518, WO 2006/012.711, GB 1.226.348, GB 1.349.732, GB 1.426.292,U.S. Pat. No. 3,490,201, U.S. Pat. No. 5,385,603 and U.S. Pat. No.8,349,054.

The drying agent or desiccant that is used in the known drying devicesfor drying compressed gas consists of silica gel, molecular sieves,activated alumina or a combination thereof, for example. As is known,the drying agent can be affixed on a support such as a corrugatedstructure of glass fibres or ceramic fibres that are rolled up forexample to form a honeycomb structure in the vessel, for example asdescribed in U.S. Pat. No. 5,683,532.

In practice it turns out that with the known drying devices for dryingcompressed gas, under certain conditions such as in the event ofinsufficient regeneration of the drying agent and oversaturationthereof, the drying agent goes through a complex breakdown process thatin some cases can ultimately result in the failure of the drying device,for example in the case of silica gel as a drying agent in a rotor,because the binder function of the silica gel decreases, which leads toa loss of structural strength of the supporting glass fibre matrix, andalso because the adsorbing function of the silica gel decreases as aresult of hydrolisation and breakdown of the silica gel structure.

Thus the adsorption behaviour and adsorption capacity of a silica gelrotor, in heavy conditions of high moisture and high temperature willsubstantially change during the useful life of the rotor.

The purpose of the present invention is to provide a method formanufacturing an improved adsorption agent for treating compressed gas,whereby this adsorption agent provides a solution to one or more of thedisadvantages attached to the conventional, known adsorption agents.

To this end the invention concerns a method for manufacturing anadsorption agent for treating compressed gas, whereby this methodcomprises the following steps:

-   -   the provision of a monolithic supporting structure;    -   the production of a coating suspension that comprises an        adsorbent;    -   the application of the aforementioned coating suspension on the        aforementioned supporting structure to form a coating;    -   the application of a thermal treatment to the supporting        structure with the coating, in order to sinter the coating.

An advantage of the adsorption agent obtained with this method is thatthere is no risk of grains moving against one another or evenfluidisation of such an adsorption agent during use in an adsorptiondevice for treating compressed gas, as loose grains of adsorption agentare not used. As a result dust formation is prevented, while arelatively high flow speed of the compressed gas to be dried through thedrying device is possible.

In addition the drying agent thus obtained enables it to be affixed in adrying device in whatever spatial orientation during use, such asvertical, sloping or even horizontal, which is not possible withconventional drying agents that are granular, as the horizontal use ofsuch granular drying agents can lead to a rearrangement of the grainsand the formation of internal leakage paths and consequently reduceddryer performance.

According to a preferred characteristic of the invention, theaforementioned monolithic supporting structure comprises one or more ofthe following materials: ceramic material, metal foil, a fibre structureand a polymer. Particularly good results are obtained with the use of aceramic structure that contains cordierite.

Preferably the aforementioned adsorbent contains one or more of thefollowing materials: a zeolite, silica gel, activated alumina, activatedcarbon, metal organic frameworks, carbon molecular sieve (CMS), animpregnated adsorbent and a hybrid. In particular a hydrophilic zeolitesupport is preferable. Good results are obtained by making use offaujasite zeolite type X, in which the silicon/aluminium ratio isbetween 2 and 3.

The present invention also relates to an adsorption agent obtained withthe method according to claim 1, whether or not in combination with thecharacteristics of one or more of the claims following on from it.

The invention also relates to an adsorption device for drying compressedgas, whereby this adsorption device comprises an adsorption agentobtained with the method according to the invention.

With the intention of better showing the characteristics of the presentinvention, a few preferred variants of a method according to theinvention for manufacturing an adsorption agent for treating compressedgas are described hereinafter by way of an example, without any limitingnature, with reference to the accompanying drawings, wherein:

FIG. 1 schematically shows a possible embodiment of a method accordingto the invention for manufacturing an adsorption means;

FIG. 2 shows a possible temperature variation that could be applied in amethod according to the invention.

FIG. 1 shows a block diagram whereby each block presents a step of themethod according to the invention and whereby in some blocks a number ofsub-steps are distinguished between.

Essentially the method according to the invention for the manufacture ofan adsorption agent for treating compressed gas consists of a step 1A ofproviding a monolithic supporting structure and a step 1B consisting ofthe production of a coating suspension that contains an adsorbent.

In the next step 2 the aforementioned coating suspension is applied tothe aforementioned supporting structure to form a coating and, finally,in step 3 a thermal treatment is applied to the resulting supportingstructure with the coating obtained after step 2, in order to sinter theaforementioned coating in order to finally obtain an improved adsorptionagent.

According to a preferred, but not necessary, characteristic of theinvention a ceramic structure that contains cordierite, for exampleCelcor© by Corning, is selected for the monolithic supporting structure.

Alternatively, according to the invention, other materials can also beused for the manufacture of the supporting structure concerned, such as:

-   -   other ceramic materials such as mullite, γ- or α-alumina or        silicon carbide (SiC);    -   metal foil;    -   a fibre structure, for example based on glass fibre, ceramic        fibre or other fibres, or a mixture of different types of        fibres; or    -   a polymer.

It goes without saying that the aforementioned list is not exhaustiveand the use of other materials is not excluded.

According to the invention, it is not excluded either that themonolithic supporting structure is made of a combination of two or moreof the aforementioned and/or other materials.

According to a preferred characteristic of the invention the materialfrom which the supporting structure is made preferably contains between200 and 1200 CPSI (cells per square inch), and more preferably between350 and 450 CPSI.

The wall thickness of the supporting structure is preferably between 2and 11 mil (milli-inch), and more preferably between 3 and 9 mil, andeven more preferably between 5 and 7.5 mil. In a most preferredembodiment, the wall thickness is between 6 and 7 mil, preferablyapproximately 6.5 mil.

The porosity of the wall of the supporting structure is preferablygreater than 5%, and more preferably greater than 10%, and even bettergreater than 20%.

The cells formed preferably have a square shape, but can present othershapes such as triangular, sinusoidal, circular, hexagonal and similar.

Step 1B of the production of the coating suspension preferably comprisesthe following sub-steps:

-   -   a first sub-step 1BX of providing a solvent;    -   a second sub-step 1BY of the addition of an adsorbent to the        aforementioned solvent to form a mixture; and    -   a third sub-step 1BZ of the addition of a binder material to the        aforementioned mixture.

In sub-step 1BY preferably one or more of the following and/or othermaterials are selected as an adsorbent:

-   -   a zeolite, preferably a hydrophilic zeolite, but a hydrophobic        zeolite is also possible—this zeolite can be faujasite zeolite        type X for example, for example Zeolum F9 of Tosoh, or a mixture        of zeolite type X and A;    -   silica gel;    -   activated alumina;    -   activated carbon;    -   metal-organic frameworks;    -   carbon molecular sieve (CMS);    -   an impregnated adsorbent; and    -   a hybrid adsorbent.

The above list is not exhaustive and other materials are also possibleaccording to the invention. The choice of adsorbent depends on whattreatment the gas to be treated must go through, such as drying or theselective removal of other molecules such as oxygen or carbon dioxidefor example, when using the adsorption means in a nitrogen generator orsimilar, whereby the gas to be treated can be compressed air forexample.

The distribution of the particle size of the adsorbent is preferablysuch that D₅₀ is less than 10 μm and more preferably less than 4 μm.

The aforementioned binder material that is added in the third sub-step1BZ preferably contains an inorganic binder material such as:

-   -   colloidal silica, for example Ludox-AS 40 of Grace Davison;    -   alumina; and/or    -   clay.

Moreover, if need be use can be made of an organic binder material suchas:

-   -   methyl cellulose;    -   polymers such as acrylic resins, vinyl resins and similar;        and/or    -   a material from the cellulose group.

According to a possible characteristic of the invention, step 1B of theproduction of the coating suspension comprises the addition of one ormore additives, such as an additive to affect the acidity (pH value),for example hydrogen chloride (HCl) to decrease the pH or ammonia (NH₃)to increase the pH, and/or an additive to counteract foam formation. Forexample, but not strictly necessary, the pH value is brought between 9and 11 and more preferably between 9.5 and 10.5.

The second sub-step 1BY of the addition of an adsorbent to theaforementioned solvent to form a mixture preferably comprises:

-   -   the introduction of the adsorbent in powder form into the        solvent    -   the mixing of the adsorbent and the solvent during or after the        introduction of the adsorbent in the solvent.

According to an additional preferred aspect of the invention, aftermixing the adsorbent in the solvent, the adsorbent particles are reducedin size in order to obtain the aforementioned preferred particle size,for example by wet milling. Examples of wet milling are attritionmilling, roll milling or immersion milling.

The coating suspension obtained after step 1B is preferably a shearthinning liquid, which upon the action of shear stress presents areduced viscosity.

Step 2 of the method according to the invention, consisting of theapplication of the aforementioned coating suspension on theaforementioned supporting structure, preferably consists of flushing orperfusing the supporting structure with the coating suspensionconcerned.

Preferably the perfusion of the supporting structure is done from bottomto top or in other words in the opposite direction to gravity, forexample by pumping means provided to this end that either pump thecoating suspension upwards through the supporting structure or sucks upthe coating suspension through the supporting structure, preferablyuntil all channels through the supporting structure have been filledwith coating material.

Then the pumping means can be switched off in order to let the surpluscoating material flow out of the channels. Alternatively the operatingdirection of the pumping means concerned can be reversed such that anactive evacuation of surplus coating material from the channels isobtained.

According to a particular preferred aspect of the invention, a part ofthe surplus coating material can be evacuated from the supportingstructure by applying one or more pressure pulses of a purge gas throughthe channels of the supporting structure. An example of such a purge gasis air.

Good results are obtained in particular when using a shear thinningcoating suspension with such active evacuation of the channels in thesupporting structure.

After any removal of surplus coating material the coated supportingstructure may be left to dry, for example in ambient conditions, untilthe solvent has largely evaporated. When water is used as a solvent, forexample, this drying can be done in the surrounding air.

In a last step 3 of the method according to the invention the resultingsupporting structure with coating, as obtained after step 2, is subjectto a thermal treatment in order to sinter the coating.

During this thermal treatment the aforementioned resulting supportingstructure is exposed to a temperature of preferably more than 400° C.,and even more preferably more than 500° C., and in a most preferredembodiment a temperature of 550° C.

Of course numerous variant temperature variations may be applied duringthis thermal treatment. A non-limiting example is shown in FIG. 2,whereby the horizontal axis shows the time expressed in hours, while thevertical axis indicates the temperature expressed in degrees Celsius.

At the start time t₀ of step three, the temperature is equal to theambient temperature, in this example 20° C. The temperature is raisedslowly, in this case at a rate of 50° C. per hour, and in this examplefor a period of 10 hours 36 minutes. At time t₁, i.e. 10 hours and 36minutes after time t₀, in this case the temperature will consequentlyhave risen to 550° C.

Preferably the period of increasing temperature is followed by a periodin which the temperature is kept constantly high, preferably above 400°C. and better above 500° C. In this non-exhaustive example the timeinterval in which the temperature is kept high is 1 hour. At the end ofthis time interval in which in this example the temperature is kept at550° C. for 1 hour, the temperature will be reduced again, in thisexample at a higher rate than the temperature increase at the beginningof the heat treatment. The temperature can be decreased for example at arate of 150° C. per hour, which in the example shown means that the timeinterval between t₂ at the end of the period in which the temperature iskept practically constantly high, and t₃ at the end of the temperaturedecrease to ambient temperature (in this example 20° C.), is only 3hours and 32 minutes.

Starting with an ambient temperature of 20° C. and by adhering to thetemperature variations as shown in FIG. 2 by way of a non-limitingexample, the entire step 3 of the heat treatment will thus take 15 hoursand 8 minutes.

As a method according to the invention yields a coating material with avery high mass density of adsorbent material and with a very goodadhesion to the supporting structure (250 kg per cubic metre or more),such an adsorption agent obtained with the method according to theinvention is extremely suitable for application in a drying device fordrying compressed gas, as the increased dryer efficiency even enablesthe flow rate of gas to be dried that is guided through the dryingdevice to be tripled. In other words, for the same flow rate of gas tobe dried, a substantially smaller drying device can be used, whichpresents important ecological and economic benefits.

In order to be able to make the layer thickness bigger, according to apreferred aspect of the invention, the steps of applying the coatingsuspension and the thermal treatment of the whole of the supportingstructure with the coating thereon is repeated one or more times, untilthe desired coating thickness on the supporting structure is reached.

The invention relates to a method for manufacturing an adsorption agent,either in the form of a drying agent for the adsorption of moisture orin the form of a different adsorption agent that can be used forselective adsorption, for example, such as in nitrogen generators orsimilar, because the adsorption agent is able to adsorb certain gasmolecules such as oxygen, carbon dioxide and similar. By removing suchgas molecules from compressed air for example, as is known, nitrogen canbe generated.

The present invention is by no means limited to the embodimentsdescribed as an example and shown in the drawings, but a methodaccording to the invention for manufacturing an adsorption agent can berealised in many ways, without departing from the scope of theinvention.

1-25. (canceled)
 26. A method for manufacturing an adsorption agent fordrying compressed gas, comprising the following steps: the provision ofa monolithic supporting structure; the production of a coatingsuspension that comprises an adsorbent, whereby for the production ofthe coating suspension an adsorbent is selected which comprises ahydrophilic zeolite; the application of the aforementioned coatingsuspension on the aforementioned supporting structure to form a coating;the application of a thermal treatment to the supporting structure withthe coating, in order to sinter the coating; whereby the application ofthe aforementioned coating suspension on the aforementioned supportingstructure comprises the step of flushing or perfusing the supportingstructure with the coating suspension concerned; whereby the perfusionof the supporting structure is done from bottom to top, or in otherwords in the opposite direction to gravity; whereby the perfusion isrealised by a pump that pumps the coating suspension upwards through thesupporting structure; whereby coating material is removed after theperfusion of the supporting structure with coating suspension; andwhereby the removal of surplus coating material is realized by reversingthe operation direction of the pump concerned.
 27. The method accordingto claim 26, wherein one or more of the following materials are selectedfor the monolithic supporting structure: ceramic material, metal foiland a fibre structure.
 28. The method according to claim 27, wherein aceramic structure that contains cordierite is selected for themonolithic supporting structure.
 29. The method according to claim 26,wherein for the production of the coating suspension one or more of thefollowing materials are selected for an adsorbent: a zeolite, silicagel, activated alumina, activated carbon, metal-organic frameworks,carbon molecular sieve (CMS), an impregnated adsorbent and a hybridadsorbent.
 30. The method according to claim 29, wherein theaforementioned adsorbent comprises faujasite zeolite type X.
 31. Themethod according to claim 26, wherein the step of producing theaforementioned coating suspension comprises the following sub-steps: theprovision of a solvent; the addition of the aforementioned adsorbent tothe solvent to form a mixture; and the addition of a binder material tothis mixture.
 32. The method according to claim 31, wherein after theaddition of the adsorbent to the solvent and the mixing of the adsorbentwith the solvent, the adsorbent particles are reduced in size by wetmilling.
 33. The method according to claim 32, wherein the particle sizeof the adsorbent is reduced in size until D₅₀ is less than 10 μm andmore preferably less than 4 μm.
 34. The method according to claim 31,wherein one or more of the following inorganic binder materials areselected as a binder material: colloidal silica; alumina; and/or clay.35. The method according to claim 31, wherein one or more of thefollowing organic binder materials are selected as a binder material:methyl cellulose; polymers such as acrylic resins, vinyl resins andsimilar; and/or a material of the cellulose group.
 36. The methodaccording to claim 26, wherein a part of the surplus coating material isevacuated from the supporting structure by applying one or more pressurepulses of a purge gas through the channels of the supporting structure.37. The method according to claim 26, wherein the aforementioned heattreatment consists of at least three phases: increasing the temperatureduring the first time interval t₁-t₀; keeping the temperature constantlyhigh at a value above 400° C. during a second time interval t₂-t₁;decreasing the temperature back to ambient temperature during a thirdtime interval t₃-t₂.
 38. The method according to claim 37, wherein thetemperature is kept constant during the aforementioned second timeinterval t₂-t₁.
 39. The method according to claim 26, wherein the stepof the production of the coating suspension comprises: the addition ofone or more additives.
 40. The method according to claim 39, wherein theaforementioned additives contain one or more of the following agents: anadditive to affect the acidity (pH value); and an additive to counteractfoam formation.
 41. The method according to claim 40, wherein theaforementioned additive to affect the acidity consists of hydrogenchloride or ammonia.
 42. The adsorption agent obtained with the methodaccording to claim
 26. 43. The adsorption agent according to claim 42,wherein it is a drying agent.
 44. The adsorption device provided with anadsorption agent according to claim
 42. 45. A method for manufacturingan adsorption agent comprising the following steps: Producing a coatingsuspension that comprises an adsorbent, wherein the adsorbent iscomprises a hydrophilic zeolite; Applying the coating suspension to asupporting structure to form a coating; and Sintering the coating by athermal treatment; Wherein said applying comprises perfusing thesupporting structure with the coating suspension, said perfusing is donein the opposite direction to gravity, and said perfusing is realised bya pump that pumps the coating suspension upwards through the supportingstructure; and further comprising Removing a portion of the coatingmaterial after the perfusing, wherein the removing is realized byreversing the operation direction of the pump.